In the semiconductor industry, chemically amplified resist (CAR) technology is essential for the fabrication of micro- and nano-size patterns. Photoacid generators (PAGs) are a key component in a CAR system, particularly for deep UV (DUV) lithography, including 248 nm and 193 nm lithography, and for next generation lithography (NGL), such as electron-beam and extreme-UV (EUV) lithography. PAGs are primarily used for lithography in the semiconductor industry but are also useful for reactive coating applications.
Several acid-catalyzed chemically amplified resist compositions are well known in the art. Chemically amplified resist compositions generally include a PAG and an acid sensitive polymer (resist). Upon exposure to radiation (e.g., x-ray radiation, ultraviolet radiation), the photoacid generator, by producing a proton, creates a photo-generated catalyst (usually a strong acid) during the exposure to radiation. The acid may act as a catalyst for further reactions during a post-exposure bake (PEB). For example, the acid generated may facilitate deprotection or cross-linking in the photoresist. Generation of acid from the PAG does not necessarily require heat. However, many known chemically amplified resists require a post-exposure bake (PEB) to complete the reaction between the acid moiety and the acid labile component. Chemical amplification type resist materials include positive working materials that leave unexposed material with the exposed areas removed and negative working materials that leave exposed areas with the unexposed areas removed.
Photoacid generators (PAGs) play a critical role in chemically amplified resist systems. Among the various classes of ionic and nonionic PAGs that have been developed, one of the most widely used classes is the perfluorinated onium salts. Government regulation has rendered many of the most effective PAGs no longer commercially viable, including those based on perfluorooctyl sulfonates (PFOS). In addition to environmental concerns, the PFOS-based PAGs are a concern because of their fluorous self-assembly and their diffusion characteristics at smaller dimensions.
Previous efforts to develop new PAGs have focused mainly on improving the photosensitive onium cation to increase the quantum yield or to improve absorbance. The nature of the photoacid produced upon irradiation of the PAG is directly related to the anion of the ionic PAG. Difference in acid strength, boiling point, size, miscibility, and stability of the photoacid produced can affect parameters related to photoresist performance, such as deprotection (or cross-linking) efficiency, photospeed, post-exposure bake (PEB) sensitivity, post-exposure delay (PED) stability, resolution, standing waves, image profiles, and acid volatility. Because PFOS-based PAGs are being phased out and current commercial PAGs have significant drawbacks with respect to the previously mentioned properties, new PAGs are needed that can help resolve these environmental and performance issues.